This invention relates to an armor structure, system, and method of providing armor.
Armor structures may be used to provide protection from projectiles that would impact vehicles, buildings, and personnel. In this context, vehicles could include ground vehicles, ships, submarines, aircraft, or spacecraft. The armor structures are often provided as a component in a laminate that comprises an armor system. The frontal member of the composite is typically present to fracture and erode impacting projectiles. A backing plate or fabric liner behind the frontal member structurally supports the frontal member and then captures the residual projectile and armor fragments.
The ceramics that are typically used in armor structures are useful materials for defeating projectiles as long as they operate in a compressive mode. For example, the compressive strength of silicon carbide (SiC) ceramic is 3,900 Mega Pascals (566,000 psi); yet the tensile strength is only 380 Mega Pascals (55,000 psi). The ratio of compressive strength to tensile strength for most metals is approximately 1 to 1, but for armor ceramics the compressive to tensile strength ratio ranges from 10 to 1 when tested in a quasi static mode to 20 to 1 when tested under dynamic conditions such as ballistic impact.
Armor is becoming an ever increasing burden to host vehicles, buildings, or personnel. This burden includes the increase in weight; the increase in space; and the cost imposed by the armor. This increasing burden is commensurate with the ever increasing threats and increasing lethality of modern projectiles.
The most common ceramic material used as armor is alumina oxide. In recent years, ceramics that are lighter than alumina oxides have been developed as armor. Newer ceramics include, but are not limited to, aluminum nitride, silicon carbide, and boron carbide. Unfortunately these newer lighter ceramics are significantly more expensive than alumina oxide.
Research has continued to develop improved grades of ceramic materials tailored to meet requirements for armored systems with the general understanding that ceramic materials that are harder and have greater fracture toughness generally perform better as armors.
Other techniques to harden a ceramic armor material have encapsulated the ceramic in a preloaded state. The preload is provided by a compressive surrounding frame, usually made of metal. The frame also holds a fractured ceramic armor in place preventing the projectile from pushing it aside and penetrating into the host object. Encapsulation of ceramic armor is a costly technique that carries several integration challenges when the design is moved from the laboratory to the host vehicle.
The armor industry measures the performance of armor with a scoring system called “mass efficiency.” Every projectile can be stopped by a certain amount of armor steel. In the armor industry, the particular alloy of steel used as the performance standard is designated Rolled Homogeneous Armor (RHA). It is a specific alloy and temper of steel defined in the US Military Standard MIL-STD-12560. The mass efficiency, designated Em, is the weight per unit area of RHA required to stop a particular threat projectile divided by the weight per unit area of the candidate armor to stop the same threat. RHA armor has an Em of 1. Some ceramic armor laminates may demonstrate better mass efficiencies against Armor Piercing (AP) projectiles than steel.
Due to weight constraints, the payload of armored vehicles is typically reduced with the addition of increased armor. Vehicle payload will continue to decrease, or the overall weight of the vehicle will have to increase, unless armor systems can be developed with significantly improved performance; with higher mass efficiencies.